High-bypass turbofan engines are used on all large jets today, including military jets. This type of engine does not produce trails unless modified with an aerosol injection system.
In 2010, we began seeing chemtrail jets (unmarked, white or silver jets) producing short trails instead of long trails. At this same time, they suddenly began flying at significantly higher altitudes (previously they flew at low altitudes). This change is obviously in response to raised public awareness about ongoing aerosol injection (spraying) programs being noticed around the world. Governments are clearly attempting to keep this activity out of public sight as much as possible.
Long Trail, Short Trail
The image below shows 2 similar jets using the same jet fuel flying at the same altitude. One jet produces a long, persistent trail while the other produces a short, non-persistent trail. Because high-bypass turbofans don't naturally produce trails, we have here a clear demonstration of the spraying of 2 different types of chemical aerosols at the same time.
The video below captures multiple jets. Two are flying in formation, which is illegal for commercial jets. One of the jets is leaving a non-persistent trail while the other is leaving no trail whatsoever. Propagandists will attempt to discredit videos like this claiming that different jet fuels may be in use. Anyone familiar with jet fuels and basic chemistry will see through such claims as propagandic.
Short, non-persistent tails are not condensation trails. High-bypass turbofan engines have a far too low fuel-to-air ratio to produce any trail except the faint, black carbon-soot trail you see at every airport. The military has updated equipment in city after city to change long trails to short, non-persistent trails to attempt to keep them from public scrutiny.
Not only are these jets in formation, they are flying at the same altitude. One jet is leaving a persistent trail while the other two are leaving non-persistent trails. All of these trails are chemical aerosols.
The photo below shows one jet with a trail and another without any trail whatsoever. Remember, the engines use the same jet fuel and operate using precisely the same principle which results in the same exhaust chemistry.